The demand for fluorescent lighting is increasing primarily because of its greater efficiency relative to other types of lighting, such as incandescent. Fluorescent lamp ballasts made with discrete components may have reduced reliability and be susceptible to problems caused by variations in circuit component tolerances and ambient conditions (e.g., temperature). Furthermore, as fluorescent lamps replace incandescent lamps, there is increased demand for fluorescent lamps to have desirable features of incandescent lamps, such as small size and dimmability. However, such features are difficult to achieve with current ballast and controller technology.
Digital control has been used in several electronic ballast applications. A digital implementation of phase control was suggested in [1]. Digitized versions of variable frequency control have also been suggested in [2] and [3]. Both control methods were applied to a half-bridge resonant inverter where totempole-connected MOSFETS were controlled. However, since half-bridge resonant inverters were used as the ballast power circuit in the above literature, only variable frequency control or phase-shift control could be used to provide basic functions while at the same time, ensure zero voltage switching (ZVS) operation.